This invention relates generally to micro-scale cavity discharge devices, and, more particularly, to generating a plasma for light emitter or chemical processing applications.
Micro-scale cavity discharge (hereinafter referred to as xe2x80x9cMSCDxe2x80x9d) devices have received considerable attention over the past years for potential application as ultraviolet (hereinafter referred to as xe2x80x9cUVxe2x80x9d) light sources and in-situ chemical processing tools. One application for UV light sources is in plasma displays wherein the UV light is used to excite a phosphor. Among the large, flat, full color, high-definition television screens or panels currently available, the gas-plasma type panel has achieved considerable success. While these panels are quite light and thin, they can produce extremely sharp pictures. Another application of micro-scale UV light emitters is in chemical and biochemical sensing by fluorescence or absorption spectroscopy.
One application for in-situ chemical processing tools is in analyzing and synthesizing a gaseous atmosphere, such as an engine exhaust or the like where it is desirable to detect and alter a chemical species. For example, a screen which includes an array of MSCD devices could be used to filter harmful chemicals from a gas flow and convert the harmful chemicals into more inert and less toxic species.
Low temperature co-fired ceramics (hereinafter referred to as xe2x80x9cLTCCxe2x80x9d) are particularly useful in the fabrication of MSCD devices because of the possibility to integrate micro-discharge devices with micro-fluidic devices and RF electronic components, which opens the door for numerous attractive applications.
Turn now to FIG. 1 which illustrates an example of a MSCD device 5 used in the prior art. In fabricating MSCD device 5, a ceramic material layer 10 is screen printed with a conductive material layer 12 and a ceramic material layer 14 is screen printed with a conductive material layer 16. Ceramic material layer 14 is positioned on conductive material layer 12 and a ceramic material layer 18 is positioned on conductive material layer 16 to form a ceramic material region 22. Region 22 is typically held together by applying a force or pressure to ceramic material region 22 so that layers 10, 12, 14, 16, and 18 are bonded together. A trench 20 is then punched through ceramic material region 22 wherein trench 20 typically has a cylindrical shape. Region 22 is then fired through a process well known to those skilled in the art.
Conductive material layers 12 and 16 function as two electrodes separated by a distance 19 which determines a breakdown voltage of MSCD device 5 wherein layers 12 and 16 are generally screen printed using a metal paste. The breakdown voltage is the voltage at which a plasma starts forming between layers 12 and 16. The area of exposed conductive regions 12 and 16 is substantially determined by a region 25 and a region 23, respectively. However, when trench 20 is punched, some of the metal paste used to screen print conductive material layers 12 and 16 is smeared in a region 21 on ceramic material layer 14 adjacent to trench 20. The smearing of the metal paste effectively changes distance 19 between conductive material layers 12 and 16 so that the breakdown voltage changes. Since the smearing is not a controllable process this leads to a lack of reproducibility of the MSCD device (i.e. the operating conditions are significantly different from one MSCD device to the next) in the discharge. Further, the metal paste used in the prior art to form layers 12 and 16 is susceptible to sputtering from electron and ion bombardment when MSCD device 5 is generating a plasma. The metal paste used in the prior art is also susceptible to oxidation which increases the breakdown voltage. Thus, the device structure and materials used in the prior art leads to unreliable performance (i.e. reproducibility and instability of the discharge and occasional failure of the plasma device to function at all) due to the smearing of the metal paste and to poor lifetime due to the sputtering of the electrodes.
Accordingly, it is an object of the present invention to provide a new and improved micro-cavity plasma discharge device with improved performance and longer lifetime.
To achieve the objects and advantages specified above and others, a micro-scale cavity device is disclosed. The MSCD device includes a micro-cavity device structure with N dielectric material structures wherein N is a whole number greater than or equal to one. Each N dielectric material structure includes a dielectric spacer region with a first opening wherein the dielectric spacer region is sandwiched between a first dielectric material region with a second opening and a second dielectric material region with a third opening. The second opening and the third opening are aligned with the first opening to form a trench with a width.
In the preferred embodiment, at least one of the first dielectric material region and the dielectric spacer region includes a first conductive layer with a surface positioned adjacent to the dielectric spacer region and an opposed surface adjacent to the first dielectric material region wherein the first conductive layer is sandwiched between the first dielectric material region and the dielectric spacer region.
In the preferred embodiment, at least one of the second dielectric material region and the dielectric spacer region includes a second conductive layer with a surface adjacent to the dielectric spacer region and an opposed surface adjacent to the second dielectric material region wherein the second conductive layer is sandwiched between the second dielectric material region and the dielectric spacer region.
In the preferred embodiment, the first conductive layer extends past one of the first dielectric material region and the dielectric spacer region into the trench to expose at least one of the surface and the opposed surface of the first conductive region. Further, the second conductive layer extends past one of the second dielectric material region and the dielectric spacer region into the trench to expose at least one of the surface and the opposed surface of the second conductive region. The first conductive layer behaves as a first electrode and the second conductive layer behaves as a second electrode.
In the preferred embodiment, the first dielectric material region, the second dielectric material region, and the dielectric spacer region include a low temperature co-fired ceramic. Further, the first and second conductive material layers include a platinum (Pt) paste.